2 Gases can expand to fill its container, unlike solids or liquids CompressibilityGases can expand to fill its container, unlike solids or liquidsThe reverse is also true:They are easily compressed, or squeezed into a smaller volume
3 CompressibilityThis is the idea behind placing “air bags” in automobilesIn an accident, the air compresses more than the steering wheel or dash when you strike itThe impact forces the gas particles closer together, because there is a lot of empty space between them.
4 Variables that describe a Gas The four variables: ( STP)1. Pressure (P) in kilopascals, 760 mmHg, 760 Torr, and 1 Atm2. Volume (V) in Liters, ml3. Temperature (T) in 273 Kelvin4. Amount (n) in moles
5 Temperature Volume Pressure Amount of space enclosed by a shape or objectMeasure of the average heat or thermal energy of the particles in a substance.PressureForce exerted on a surface per unit area.
6 1. Amount of GasWhen we inflate a balloon, we are adding gas molecules.Increasing the number of gas particles increases the number of collisionsthus, the pressure increasesIf temperature is constant, then doubling the number of particles doubles the pressure
7 2. Volume of GasIn a smaller container, the molecules have less room to move.The particles hit the sides of the container more often.As volume decreases, pressure increases. (think of a syringe)Thus, volume and pressure are inversely proportional to each other
8 3. Temperature of GasRaising the temperature of a gas increases the pressure, if the volume is held constant. (Temp. and Pres. are directly proportional)The molecules hit the walls harder, and more frequently!
11 1. The volume of a gas particle is miniscule compared to the distance between themselves and other molecules.2. Gas particles undergo no intermolecular attractions or repulsions.3. Gas particles are in continuous, random motion.4. Collisions between gas particles are perfectly elastic.5. The average kinetic energy is the same for all gases at a given temperature, regardless of the identity of the gas.
14 Boyle’s LawGas pressure is inversely proportional to the volume, when temperature is held constant.Equation: P1V1 = P2V2
15 Graph of Boyle’s Law – page 418 Boyle’s Law says the pressure is inverse to the volume.Note that when the volume goes up, the pressure goes down
16 A balloon contains 7. 2 L of He. The pressure is reduced to 2 A balloon contains 7.2 L of He. The pressure is reduced to 2.00 atm and theballoon expands to occupy a volume of 25.1 L. What was the initial pressureexerted on the balloon?
18 Charles’s LawThe volume of a fixed mass of gas is directly proportional to the Kelvin temperature, when pressure is held constant.Temperature Must Be in Kelvin.
19 Converting Celsius to Kelvin Gas law problems involving temperature will always require that the temperature be in Kelvin. (Remember that no degree sign is shown with the kelvin scale.)Kelvin = C + 273°C = Kelvin - 273
20 A balloon is filled with 3. 0 L of helium at 310 K A balloon is filled with 3.0 L of helium at 310 K. The balloon is placed in an oven where the temperature reaches 340 K. What is the new volume of the balloon?
22 Gay-Lussac’s LawThe pressure and Kelvin temperature of a gas are directly proportional, provided that the volume remains constant.
23 #4. The Combined Gas LawThe combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.
24 The equation for Avogadro's Law is V/n=k The equation for Avogadro's Law is V/n=k. V is the volume of the gas, n is the amount of substance of the gas, and k is a proportionality constant.
25 5. 00 L of a gas is known to contain 0. 965 mol 5.00 L of a gas is known to contain mol. If the amount of gas is increased to 1.80 mol, what new volume will result (at an unchanged temperature and pressure)?
26 Dalton’s Law of Partial Pressures For a mixture of gases in a container,PTotal = P1 + P2 + PP1 represents the “partial pressure”, or the contribution by that gas.Dalton’s Law is particularly useful in calculating the pressure of gases collected over water.
27 = 6 atm Sample Problem 14.6, page 434 If the first three containers are all put into the fourth, we can find the pressure in that container by adding up the pressure in the first 3:2 atm+ 1 atm+ 3 atm= 6 atm1234Sample Problem 14.6, page 434
28 8. Graham’s Law RateA MassB RateB MassA = The rate of effusion and diffusion is inversely proportional to the square root of the molar mass of the molecules.Derived from: Kinetic energy = 1/2 mv2m = the molar mass, and v = the velocity.
34 Ideal Gases don’t exist, because: Molecules do take up spaceThere are attractive forces between particles- otherwise there would be no liquids formed
35 Real Gases behave like Ideal Gases... When the molecules are far apart.The molecules do not take up as big a percentage of the spaceWe can ignore the particle volume.This is at low pressure
36 Real Gases behave like Ideal Gases… When molecules are moving fastThis is at high temperatureCollisions are harder and faster.Molecules are not next to each other very long.Attractive forces can’t play a role.
37 Diffusion is:Molecules moving from areas of high concentration to low concentration.Example: perfume molecules spreading across the room.Effusion: Gas escaping through a tiny hole in a container.Both of these depend on the molar mass of the particle, which determines the speed.
38 Diffusion: describes the mixing of gases Diffusion: describes the mixing of gases. The rate of diffusion is the rate of gas mixing.Molecules move from areas of high concentration to low concentration.Fig , p. 435
39 Effusion: a gas escapes through a tiny hole in its container -Think of a nail in your car tire…Diffusion and effusion are explained by the next gas law: Graham’s
40 Graham’s LawSample: compare rates of effusion of Helium with Nitrogen – done on p. 436With effusion and diffusion, the type of particle is important:Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.Helium effuses and diffuses faster than nitrogen – thus, helium escapes from a balloon quicker than many other gases!